Radio adapter unit



March 26, 1946.

FIG. 1.

Filed Sept. 13, 1944 3 Sheets-Sheet 1 A-F OUTPUT DPVIZ l4 1 7 I6 l5 u n I" L I" I7 M 5+ 2| 1 H :9 l 24' 21 11: is

50 24 l. I 4 l:

19 \IB R-F INPUT SI% %25 2Q %26 %/4 -F 52\ L.- 7- 4 AA r x1. if CONVENTIONAL I I RADIO 4 RECEIVER v INVENTORS.

EUGENE COLE ROBERT E. M COY ATTORNEY March 26, 1946. COLE ETAL 2,397,128

RADIO ADAPTER UNIT Filed Sept. 13, 1944 3 Sheets-Sheet 2 FIG. 2.

PLATE VOLTAGE B TUBE l8 PLATE VOLTAGE C TUBE l9 UNMODULATED A A A A A A A AA A A A A A A A CTHODE VOLT GE MM y 1 y y y y y y y 1y 1 1 IvfULTIVIBRATOQ n MODULAT ED F LOOP-SENSE VOLTAGE RECEIVER OUTPUT G SE NSE VOLTAGE INVENTOR. EUGENE COLE ROBERT E. M COY ATTORNEY March 26, 1946.

LOOP VOLTAGE A (OUT OF PHASE) UNMODULATED CATHODE VOLTAGE MULTIVIBRATOR l7 MODULATED LOOP-SENSE VOLTAGE RECEIVER OUTPUT D 'E. COLE ETAL RADIO ADAPTER UNIT Filed Sept. 13, 1944 FIG. 3.

3 Sheets-Sheet 5 VVVVVVVVVVVVVVVV INVENTOR. EUGENE COLE ROBERT E. MCCOY Ww, M,

ATTORNEY Patented Mar. 26, 1946 UNiTD ST RADIO ADAPTER UNIT Application September 13, 1944, Serial No. 553,850

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 6 Claims.

The invention described herein may be manufacture'd and used by or for the Government for governmental purposes, without the payment to us of any royalty thereon.

Our present invention relates to radio direction-finding systems, and more particularly, to an adapter unit which, when used in conjunction with a standard radio receiver, forms a system of the general character indicated.

It is the main object of our present invention generally to improve the art of radio direction finding by providing a simpl and inexpensive adapter unit which, when used as aforesaid,

enables a highly accurate determination of the direct bearing of any source of radio-frequency energy to which the associated receiver is capable of being tuned.

It is another object of our present invention to further improve the art of radio direction finding by eliminating the need for the hitherto used galvanometer and oscilloscope-type indicators; providing instead, a simple and inexpensive electron-ray indicatorysuch as a magic-eye tube.

These, and other obiects and advantages of our present invention, which will be better understood as the detailed description thereof progresses, are attained in the following manner: a Our adapter comprises, generally, a loop antenna, a vertical sense antenna, a multivibrato'r, a synchronous rectifier, and a twin-eye, electronray indicator tube.

The oppositely-phased outputs at the terminals of the loop antenna are alternately combined with the" output of the sense antenna. This is accomplished by applying said loop antenna outputs to the grids of th respective tubes of the multivibraton'and by applying said sense antenna output to the tied cathodes of said tubes. The multivibrator oscillates at a low audiofrequencyrate, thereby acting as an electronic switch which, in effect, causes voltages proportiona1 to-the loop antenna outputs to be alternately added to and subtracted from the sense antenna output. The combination of the loop and. vertical sense antenna outputs results in a mor or less cardioid antenna response pattem, and the switching effected by the multivi-brator results in said pattern being shifted from one side to the other of the null of the loop in synchronism with the ,mu'ltivibrator .oscillations. The combined output at the tied cathodes of the multivibrator is, therefore, .an audio-frequency modulated, radio-frequency sisnal the polarity of whose modulation envelope is a function of the direct bearing of the source of the received radio-frequency signal.

Said output is applied to a standard radio receiver, and the audio-frequency modulation is thereby recovered therefrom.

The resulting audio signal is then applied simultaneously to the grids of both tubes of the synchronous rectifier.

Said synchronous rectifier tubes are biased so that they normally barely conduct, and have applied thereto a portion of the plate outputs of the multivibrator, whereby said tubes become, alternately, biased beyond cutoff biased somewhat above cutoff.

Now, the recovered audio Signal which, as stated, is also applied to said synchronous rectifier, will have either the same or opposite polarity as the switchin voltage applied to the tubes of said synchronous rectifier inasmuch as both are produced by the same multivibrator action. The tube at which the recovered audio and switching voltages are of the same polarity, that is, in phase will, therefore, conduct more freely, while the remaining tube will conduct less freely. Thus, the average plate current of one tube will increase, While the other decreases, and the corresponding plate voltages will change oppositely, by an amount depending upon the amplitude of the recovered audio signal.

Each plate of the synchronous rectifier is connected to one of the deflecting vanes of the twineye, electron-ray indicator tube, so that the eye controlled by one tube will remain substantially closed (or attempt to close further, or overlap), but the eye controlled by the other tube will open.

As stated, the polarity of the detected audio signal is a function of the direct bearing of the source of the received radio-frequency signal. In other words, said polarity depends upon the side of the null to which the loop is instantaneously turned, each side producing a modulation envelope which is mutually out of phase. When, however, the loop is in its null position, there is no loop output, and therefore no modulation by the multivibrator of the signal introduced into the receiver. The switching voltages applied from the multivibrator to the synchronous rectifier, actin alone, produce substantially equal average potentials at the plate of each tube of said synchronous rectifier; and these potentials are initially adjusted to the threshold potentials of each eye. Consequently, when the loop is in its null position, both eyes of the indicator tube remain substantially closed,

and the operator is thereby advised that the null of the loop is oriented to the bearing of the source of the radio-frequency signal to which the equipment, at the moment, is tuned.

A scale, calibrated in azimuth, is rotatable with the loop, and. by orienting the loop appropriately with respect to some predetermined reference direction, the bearing of the received signal may be read directly on said scale immediately the loop is turned to the null position.

In the accompanying specification there is described, and in the annexed drawings shown, what is at, present considered a preferred embodiment of the direction-finding system of our present invention. It is, however, to be clearly understood that our present invention is not limited to said embodiment, inasmuch as changes therein may be made without the exercise of invention and within the true spirit and scope of the claims hereto appended.

Insaid drawings,

Figure 1 is a circuit diagram of an adapter unit assembled in accordanc with the principles of our present invention;

Figure 2 shows the wave shapes resulting from the various components of our adapt-er unit, assuming a certain direction of propagation of the received radio-frequency signal, and also showing the resultin indicator display; and

Figure 3 shows the wave shapes assuming a direction of propagation opposite to that assumed in Figure 2, together with the resulting indicator display under this altered condition, and also under an "on target condition.

Referring now more in detail to the aforesaid preferred embodiment of the adapter unit of our present invention, with particular reference to Fig. 1 of the drawings, the numeral ill designates a loop antenna the terminals of which are connected to slip rings ii and 2 which, in turn, wipingly engage contacts l3 and i l.

The contacts 53 and i i are respectively connected to the stators of a pair of ganged variable capacitors l5 and ['6 whose rotors are grounded, as shown.

The numeral I"! generally designates a multivibrator, which includes a pair of triode vacuum tubes l 8 and it. These tubes may be separate, or may be in a single envelope. The cathodes of said tubes are grounded through a common resistor 26, and the plates thereof are connected, through resistors 2i and 22, to an appropriate B-voltage supply. Feedback from the tube ill to the tube 19 is accomplished, through a coupling capacitor 23 and R.-F. blocking and currentlimiting resistor 24, which is by-passed for R. F. by a capacitor 24, across a grounded grid resistor 25; and feedback from the tube H) to the tube I8 is similarly attained, through a coupling capacitor 26 and R.-F. blocking and current-limiting resistor 27, which is by-passed for R. F. by a capacitor 27, across a grounded grid resistor 28. The multivibrator oscillates, preferably, at a low sistor 20 of the multivibrator. The purpose of the resistor 32 is to assure the current in the vertical antenna 3| being in phase with its voltage.

The combination of the loop and sense anten-.

nae outputs across the cathode resistor 20 of the multivibrator results in a radio-frequency signal,

of said signal is a function of modulated at the audio-frequency rate of the 'multivibrator, and, as will later be more fully ex-' from.

. The audio output of the receiver 34 is applied, through a coupling capacitor 35, to a synchronous rectifier generally designated by the reference character 36.

Said synchronous rectifier includes a pair of triode vacuum tubes 31 and 38 the cathodes of which are grounded through a common resistor 39, by-passed by a capacitor 40. Said tubes may be separate, or in a single envelope. Plate voltages are applied to said tubes through a centertapped resistor 4 l, by-passed by capacitors 42 and.

t3, and the grids thereof are connected, through voltage-dividing networks including isolating resistors 44 and 45 and a potentiometer 46, and through a common resistor 41, to ground.

The grid of the tube 3'! is receptive, through a coupling capacitor 48 and an isolating resistor 49, of the plate output of the tube ill of the multivibratorll, and the gridof the tube 38 is receptive, through a coupling capacitor 50 and an isolating resistor 5|, of the plate output of the tube I9 of said multivibrator.

The purpose of the isolating resistors 44 and 45 is to so isolate the grids of the synchronous rectifier tubes from the receiver output that the audio-frequency rate, and inasmuch as the tubes thereof are alternately conducting, it constitutes an electronic switch. I

The tubes l8 and I9 are respectively receptive. through coupling capacitors 29 and 30, of the oppositely-phased output voltages of the loop I!) appearing across the tuning capacitors l5 and It.

A vertical sense antenna 3| is associated with the loop I0, and the output thereof is combined alternately with the oppositely-phased outputs of said loop by connecting the same, through a resistor 32, to the upper end of the cathode relatter does not have exclusive control over the grid voltages, and similarly, the purpose of the isolating resistors 49 and 5| is to so isolate the grids of the synchronous rectifier tubes from the plates of the 'multivibrator tubes that the latter do not have exclusive control over said grid voltages.

Normally, there is a balanced output from the synchronous rectifier. The switching voltages applied thereto from the multivibrator cause the tubes 31 and 38 alternately to draw plate current which, passing through the cathode resistor 39, maintains the tube not then receiving the positive half of its switching voltage biased beyond cutoif. At the same time, the tube which is receiving the positive half of its switching voltage is brought toa point above. cutoff. Thus. the switching voltages alone bring about a moderate plate-current fiow. in the synchronous rectifier circuit. By adjustment of the tap on resistor 46, the average D.-C. potentials of the two plates are made substantially equal The synchronous rectifier output is utilized to control the operation of an electron-ray indicator, such as a twin-eye tube 52. Two singleeye tubes may be used if desired. The plate cutput of the rectifier tube 31 is applied to the right deflecting vane of the tube 52, and the plate output of the rectifier tube 38 is applied to'the left deflecting vane of said tube. The cathode of the indicator tube is grounded, and the target thereof is connected to the B-voltage supply. I

While we do not deem it necessary to show it in the drawings, a tuned circuit might, if desired, be inserted between the output of the receiver 34 and the input to the synchronous rectifier-3B so as to remove from the receiver output any modulation included in the radio-frequency signals on which bearings are taken. Such a circuit will reduce spurious response or blinking of the indicator eyes. If further desired, the tuned circuit may be combined with an audio amplifier 2H, and we shall further assume that initially, the

tube l8 oi the multivibrator I! is conductin while the tube i9 is not, as may be seen from the plate voltage waves shown in Figures 23 and 2C.

The loop antenna output, shown in Figure 2A, appears across the tuning capacitors l and I6 as two oppositely-phased voltages which are applied to the respective grids of the tubes l8 and d IH. Inasmuch as the tube i8 is then conducting, the loop output appears across the cathode resistor 26 as shown in the first half-cycle display of Figure 21). When the tube I8 ceases to conduct, thetube it starts to conduct, and inasmuch as the inputs to the tubes i8 and i9 are in phase opposition, the loop output now appears across the cathode resistor as shown in the second halfcycle .display of Figure 2D. Continued switching of the tubes Iii and I9 results in the cathode resistor outputs shown in the third and fourth halfcycle displays of Figure 13, and so on.

Now, the output of the sense antenna, of somewhat greater amplitude than that of the loop, as shown in Figure 2E, is also applied across the cathode resistor 2i], and the combination of this voltage with the voltages obtained from the above-described switching'operations, results in the modulated voltage shown in Figure 2F.

Applying this modulated voltage to the receiver 34 results in recovering the envelope shown in Figure 2G.

At this point. it is thought advisable to turn to Figure 3 in order to observe the loop voltage, the

cathode resistor output before modulation, the

modulated output resulting from a combination of the loop and sense antennae voltages, and the recovered modulation envelope, respectively shown in Figures 3A, 3B, 3C, and 3D, when the direction of propagation of the radio-frequency signal instantaneously being received is, as shown by the arrow at the left of the cardioid antenna pattern display of Figure 3E, opposite to that shown in Figure 2H. It is to be particularly noted that the modulation envelopes of Figures 2G and 3D are of opposite polarity, in other words, displaced 180 with respect to each other.

Now returning to Figure 2, it will be observed that the receiver output is of the same polarity as the plate voltage of the multivibrator tube I9. Therefore, with the direction of propagation as originally assumed, tube 38 of the synchronous rectifier 36 draws more plate current than tube 31; the potential of the left deflecting vane of the indicator tube 52 drops; and the left eye opens. The potential of the right deflecting vane rises, but this has little effect since the right eye is already closed, as shown in Figure 21-1. Such a display advises the operator that the loop, and the calibrated scale carried thereby, should be rotated to the right.

If the direction of propagation of the received radio-frequency signal had been as assumed in connection with Figure 3E, then the right eye would have opened and the left eye remained closed. It would then be necessary to rotate the loop to the left.

If the plane of the loop is perpendicular to the direction of propagation of the received radiofrequency signal, in other words, the loop is in its null position, there is no loop output, and therefore, no modulation due .to the multivibrator. No audio signal is obtained from the receiver, and the synchronous rectifier remains balanced. Both eyes of the indicator tube remain closed, as shown in Figure 3F, and the operator is advised thereby that the loop is oriented to its on target position.

This completes the description of the mode of operation of the radio direction-finding system of our present invention. It will be noted that said system results from the combination of a simple adapter unit with a standard radio receiver. The adapter unit incorporates a simple direct bearing indicator, which requires no special power supply, no special skill in utilizing the same. and is rugged and inexpensive.

Other objects and advantages of our present invention will readily occur to those skilled in the art to which the same relates.

We claim:

1. In a radio direction-finder: an antenna sys tem having a more or less cardioid response pattern; means for periodically switching the direction of said response pattern through. whereby, when the bearing of the source of the received energy is in a direction other than that perpendicular to the plane of said antenna system, the output of said antenna. system becomes modulated at a frequency corresponding to the rate of said switching, and the polarity of the resulting modulation envelope becomes a function of said bearing; means for recovering said modulation envelope: a twin-eye indicator tube; and means, operable under the joint control of the output of said switching means and said modulation envelope, and responsive to the relative polarities thereof, for operating one or the other of the eyes of said indicator tube, depending upon which side of said perpendicular said bearing lies.

2. In a radio direction-finder: an antenna system having a more or less cardioid response pat tern; means for periodically switching the direction of said response pattern through 180 whereby, when the bearing of the source of the received energy is in a direction other than that perpendicular to the plane of said antenna system, the output of said antenna system becomes modulated at a frequency corresponding to the rate of said switching, and the polarity of the resulting modulation envelope becomes a function of said bearing; means for recovering said modulation envelope; a twin-eye indicator tube; and a synchronous rectifier, operable under the joint control of the output of said switching means and said modulation envelope, and respdnsive to the relative polarities thereof, for operating one or the other of the eyes of said indicator tube, de-

pending upon which side of said said bearing lies.

3. In a radio direction-finder: an antenna system having a more or less cardioid response pattern; means for periodically switching the direction of said response pattern through 180 whereby, when the bearing of the source of the received energy is in a direction other than that perpendicular to the plane of said antenna system, the output of said antenna system becomes modulated at a frequency corresponding to the rate of said switching, and the polarity of the resulting modulation envelope becomes a function of said bearing; means for recovering said modulation envelope; a twin-eye indicator tube; and a synchronous rectifier including a pair of vacuum tubes each of which is adapted to control the operation of one of the eyes of said indicater tube, said synchronous rectifier tubes being receptive of the output of said switching means whereby each is alternately biased above and below cutoif, and each is receptive of said modulation envelope, whereby the instantly conducting tube at which the output of said switching means and said modulation envelope have the same polarity, become more conducting.

a. In a radio direction-finder: an antenna system having a more or less cardioid response pat tern; a multivibrator circuit receptive of the output of said antenna system for periodically switching the direction of said response pattern perpendicular through 180 whereby, when the bearing of the source of the received energy is in a direction other than that perpendicular to the plane of said antenna system, the output of said antenna system becomes modulated at a frequency corresponding to that of the oscillations of said multivibrator circuit, and the polarity of the resulting modulation envelope becomes a function of said bearing; means for recovering said modulation envelope; a twin-eye indicator tube; and means, operable under the joint control of the output of said multivibrator circuit and said modulation envelope, and responsive to the relative polarities thereof, for operating one or the other of the eyes of said indicator tube, depending upon which side of said perpendicular said bearing lies.

5. In a radio direction-finder: an antenna system having a more or less cardioid response patenvelope; a twin-eye indicator tube; and a synchronous rectifier, operable under the joint control of the output of said multivibrator circuit-- and said modulation envelope, and responsive to the relative polarities thereof, for operating one or the other of the eyes of said indicator tube, depending upon which side of said perpendicular said bearinglies.

6. In a radio direction-finder: an antenna system having a more or less cardioid, response pattern; a multivibrator circuit receptive of the output of said antenna systemfor periodically switching the direction of said response pattern through whereby,

other than that perpendicular to the plane of said antenna system, the output of said antenna system becomes modulated at a frequency corresponding to that of the oscillations of said multivibrator circuit, and the polarity of the resulting modulation envelope becomes a function of said bearing; means for recovering said modulation envelope; a twin-eye indicator tube; and .a simchronous rectifier including a pair of vacuum tubes each of which is adapted to control the operation of one of the eyes ofJsaid indicator tube, said synchronous rectifier tubes being recaptive of the output of said multivibrator circuit whereby each is alternately biased above and below cutoff, and each is receptive of said modulation envelope, whereby the instantly conducting tube at which the output of said switching means and said modulation envelope have the same polarity, becomes more conducting.

EUGENE COLE. ROBERT E. MCCOY.

when the bearing of the source of the received energy is in adirectimi 

